Process for the purification of benzene



March 18, 1958 A. scHMALENBAcl-x 2,827,504

PROCESS FOR 'HE PURIFICATION OF BENZEN Filed Jan. 27, 1955 .H mm/.N may@ @fw .5@ M wy, 4B

United PROCESS FOR THE PURHCATION OF BENZENE Application January 27, 1955, Serial No. 484,521

6 Claims. (Cl. 260-674) The present invention relates to a process for the puriiication of crude benzene by catalytic treatment of crude benzene with hydrogen or a hydrogen-containing gas at increased pressure and increased temperature (pressure refining).

It is known that the impurities present in crude benzene, especially unsaturated, resin-forming hydrocarbons as well as sulfur and nitrogen compounds can be separated by owing the benzene in the vapor phase with hot hydrogen over suitable catalysts, whereby a saturation of the unsaturated compounds or a hydrogenation of the sulfur and nitrogen compounds to hydrogen sulfide or ammonia is effected. After separation from the impurities of the new compounds formed, a benzene of a high degree of purity is obtained.

This principal process has been carried out in practice by various means, especially with respect to means for heating the benzene and the hydrogen-containing gas to operating temperature. C For example, it has been suggested to heat the crude benzene and the hydrogen-containing gas separately in indirect heaters whereby the essentially hot hydrogen gas is` used to Vvaporize the less heated liquid benzene.

It has Ybeen further suggested to mix the hydrogencontaining gas, which can for example be fairly pure hydrogen or coke-oven gas, or the like, with the liquid crude benzene after the compression and to transfer the mixture to an indirect heat exchanger at increased temperature, for example, to a temperature above 180 C.

vThe first-named method, namely, to heat separately in indirect heat exchangers the benzene and hydrogen gas leads Yto diiculties when standard coal distillation gas is used as hydrogen-containing gas, which as is known, contains resin-forming constituents, for example, nitric oxide.v lf coke oven gas is heated, as it is produced in coke plants, indirectly to higher temperatures, for example, to 300 C., incrustations are formed on the walls of the heater which linally lead to an obstruction of the pipelines. .Y

The second named measure, namely, mixing the liquid benzenerst with the hydrogen-containing gas and heating the mixture in an indirect heat exchanger has a certainv advantage over the rst cited process but is not always completely satisfactory. The mixing of the hydrogen gas and liquid benzene can not always be eifected fSO homogeneously that largergas bubbles are not formed which "can causepoints of local overheating on passing through the indirect heater at which encrustations of high boiling or insoluble materials are deposited which finally cause interruption in operation.

The present invention solves the problem of completely or practically completely preventing depositions which can form on indirect heating both from the hydrogencontaining gas as well as also from the benzene.

The process of the present invention comprises essentially contacting or washing the hydrogen-containing gas, while avoiding any indirect addition of heat to said gas, with hot liquid benzene the temperature of which is atent higher than that of the gas; separating 'the hydrogencontaining gas washed with benzene liquid and thereby heated by the benzene liquid without substantially vaporizing the latter; and iinally subjecting the benzene to a hydrogenation treatmentin the Vapor phase in known manner. A Y Y By the direct transfer of heat from the hot, but liquid, benzenevto the hydrogen-containing gas the temperature of the hydrogen-containing gas is increased on the one hand, and this gas is also simultaneously washed with liquid` ,benzeneV whereby the resin-forming constituents in the gas are washed out and are dissolved in the benzene. These Vresin-forming constituents by subsequent polymerization treatment, the polymerization resulting from the benzene hydrogenation step. Y

ln practice, the dir/ect heat exchange between liquid benzene and the hydrogen-containing gas is, for example, carried out in such manner that the gas is introduced at the bottom of a washer provided with heat-exchange material, or the like, and thehot, liquid benzene is added at the top whereby the gas and liquid flow countercurrently to one another.

A modiiication of the process of the present invention is illustrated schematically in the accompanying drawing.

The crude benzene is owed from line 2 into compressor 4 where it is brought essentially to the subsequently Voperating pressure. After flowing through the heat `exchanger 6 the liquid benzene arrives, at a temperature of about 190 C., in the indirect heat exchanger or washer 8. The latter contains a packing 16, for example, Raschig rings, or the like.

The fresh gas, for example, coke oven gas, continuously necessary fory the refining is flowed through line 12 through compressor 14 and line 16 at a temperature of about C., into the bottom of washer 8 and cornes in contact in packing 10 with the liquid benzene. The temperature of the coke oven gas is thereby increased to to 190 C., whereas the temperature of the benzene falls to Y175 to about 170 C. VThe benzene is withdrawn from the washer through line 18 and is heated to a temperature of 200 C. in heater 20which is inthe circuit along with a diphenyl heater to be described Iater, and finally ows in polymerization furnace 22Vin which the liquidbenzene remains for a certain time in order to make possible the formation of high boiling polymers from certain impurities of the benzene. The still liquid benzene is iiowed through line 24 into vaporizer 26. In vaporizer 26 the fresh gas withdrawn from washer 8 through line 23 is simultaneouslyY added through line 30. Furthermore, the recirculated cokeAoveu gas or hydrogen gas, which is separated from the purified benzene at the end of the process, and is then again heated in heater 31, is owed into vaporizer 26 through line 30. The vaporizer is likewise provided with line 32 and line 34 for indirect heating (steam, diphenyl). By the effect of the hot coke oven gas on the one hand and the indirect heating medium on the other, the benzene is vaporized whereby a high boiling product is formed inV the bottom of vaporizer 26 which contains the polymer, including a `certain amount of benzene, which product ist withdrawn through line 36. rThe mixture of benzene vapors and coke oven gas is withdrawn from the vaporizer through line 38 at a temperature of about and after being heated in heat exchanger and eater 42 is brought to a temperature of 320 C. Thereafter, the mixture of gas and benzene is owed in the actual contact or refining furnace 44 wherein unsaturated compounds still contained in the benzene as well as the sulfur and nitrogen compounds are hydrogenated. The mixture of vapors leaves the contact furnace through line de at a temperature of about 550 C., is passed through through heat exchangers 40 and 6, and finally reaches Y cooler 4S in which the temperature of the mixture is decreased to such extent that purified benzene is'precipitate'd in liquid form, which is then collected in receiver 50 and caribe withdrawn through line 5 2. The hydrogencontaining ygars is .withdrawn `*from receiver 50 Qthroug'n line 54. A part of this gas, after-.expansion in ,valve S6 is returned to the main gasline while'pthegreater-part is recirculated through line 5S through a compressor 60, heaterV 31, line and again into vapo'rizer 26. The

heaters 20, V31 and 42-are inthe circuit V,of a Vheating media circulation system which consists of an organic heating media, for example, diphenyl, which is maintained heated byY means of heater 62 and'in circulation by means of pump 64. Y

The term without substantial vaporiza'tio'n? means, within the scope of the present invention, only the vaporization which would be effected by an addition of indirect heat to direct heat exchanger or washer 8. Such a.vapori zation is to be maintained optionally small. Independently thereof there naturally occurs a type of evaporation of a part of the benzene by virtue of the saturation'by the Y hydrogen gas flowed through line 16 with thebenzene c tained at 'an elevated temperature and pressure for a sustained period of time, removing ythe benzene and Vlow boiling VVimpurities as vapors from'rsaid polymers'while leaving said polymers to remain as liquid residue, hydrogenating said vapors, and removing the Vbenzene from the products of said hydrogenation, said improvement comprising treating said crude benzene prior to said polymerizing step by contacting a hydrogen-containing coke oven gas Vwith said crude benzene while said crude benzene .is a 'hot liquid whose temperature is higher than that of the gas and while anyindirect Vtransfer of heatto said. gas is avoided so that said gas is heatedby directtransfer of heat from theliquidtothe gas and is washed with'the liquid, separating the said gas from lsaid liquid without substantial vaporization of said liquid,,andthereafterusing said liquid as the crude-benzol for said polymerizing-and said gas for hydrogenating-said vapors.

, 2. The improvement in accordance with ,claim 1 wherein the contacting of the hydrogen-containing coke oven gas withV the hot, liquid, crude benzene is effected by bottom of said column, and tiowingV said liquid benzene downwardly and said gas upwardly in said column'in countercurrent contact with one another, whereby the temperature of said gas within said column is increased to within the range of from l85to 190 C. and the temperature of said liquid benzene .within said column Vis simultaneously decreased to within the range of from 175 to 170 C.

4. *In a process for the purification of vcrude benzene containing Yunsaturated hydrocarbons and sulfur :compounds as impurities Vand comprised of the stepsV of/maintaining said crude benzene in the liquid phase at an elevated temperature and at superatmospheric pressure for a period sufficient to polymerize any polymerizableirnpurities thereof to resinouscompounds of higher boiling point than benzene, vaporizing benzene hydrocarbons and other low boiling constituents while said compound remains Ain the liquid phase, reacting the vapors so obtained with coke `oven gas atan elevated temperature and kat superatmospheric pressure and inthe presenceV ofV a cata-VV lyst to hydrogenate any unsaturated'hydrocarbons andl sulfur compounds contained in the vapors being treated,V

and thereafter separating benzene lfrom the reactionV Vapors and catalyst, the improvement which comprises treating said crude benzene prior to the aforesaid rst step ofA 5. The process in accordance with claim-@4 ywherein the contacting of the coke oven gas 'withthe hotliquid crude benzene is elfected by adding said liquid toa packed washer column at the top thereof, adding saidgas to said column at the bottom thereof, and ilowing saidliquid downwardly and said` gas upwardly in said column in countercurrent contact with one another.

6. The process in accordance with claim 4 wherein theY contacting of the coke oven gas with'the hot, liquid, crude benzene is effected by adding said liquid ata temperatureof from 190 Yto 195 C. to a packed'washercolumn at the top thereof, adding said gas ata temperature of from to 120 C. to said column at'the bottom thereof, and flowing said liquid downwardly'and rsaid gas upwardly in said column in countercurrent contact with one another, whereby thertemperature'of the said gas is increased to from about 185 to about 190 C. andV the temperature of said liquid is decreased-to from 1754 to C. I

References Cited in the le of this patent UNITED'STATES PATENTS 

1. AN IMPROVEMENT IN A PROCESS FOR THE PURIFICATION OF CRUDE BENZENE CONTAINING UNSATURATED HYDROCARBON AND SULFUR IMPURITIES BY POLYMERIZING THE IMPURITIES WHICH WILL POLYMERIZE TO POLYMERS WHEN SAID CRUDE BENZENE IS MAINTAINED AT AN ELEVATED TEMPERATURE AND PRESSURE FOR A SUSTAINED PERIOD OF TIME, REMOVING THE BENZENE AND LOW BOILING IMPURITIES AS VAPORS FROM SAID POLYMERS WHILE LEAVING SAID POLYMERS TO REMAIN AS LIQUID RESIDUE, HYDROGENATING SAID VAPORS, AND REMOVING THE BENZENE FROM THE PRODUCTS OF SAID HYDROGENATION, SAID IMPROVEMENT COMPRISING TREATING SAID CRUDE BENZENE PRIOR TO SAID POLYMERIZ ING STEP BY CONTACTING A HYDROGEN-CONTAINING COKE OVEN GAS WITH SAID CRUDE BENZENE WHILE SAID CRUDE BENZENE IS A HOT LIQUID WHOSE TEMPERATURE IS HIGHER THAN THAT OF THE GAS AND WHILE ANY INDIRECT TRANSFER OF HEAT TO SAID GAS IS AVOIDED SO THAT SAID GAS IS HEATED BY DIRECT TRANSFER OF HEAT FROM THE LIQUID TO THE GAS AND IS WASHED WITH THE LIQUID, SEPARATING THE SAID GAS FROM SAID LIQUID WITHOUT SUBSTANTIAL VAPORIZATION OF SAID LIQUID, AND THEREAFTER USING SAID LIQUID AS THE CRUDE BENZOL FRO SAID POLYMERIZING AND SAID GAS FOR HYDROGENATING SAID VAPORS. 